Examples of such a conventional apparatus include an inkjet printing apparatus having an inkjet printing head, an inspecting unit, and a controller. See, for example, Japanese Patent Publication No. 2010-42629A.
The inkjet printing head is constituted by a plurality of printing modules arranged in a width direction (primary scanning direction) of web paper, the width direction being orthogonal to a transportation direction of the web paper. Moreover, in a construction for color printing, printing heads for black (K), cyan (C), magenta (M), and yellow (Y) are arranged in this order from upstream in the transportation direction of the web paper.
The controller controls the printing heads so as to print a correcting chart onto the web paper, and capture the correcting chart while locating the correcting chart at the inspecting unit. Thereafter, the controller determines step shift of the printing head for black (K) in the transportation direction in accordance with the correcting chart, thereby determining correction data for correcting the step shift. Then, the controller applies the correction data upon printing with the printing head for black (K) to print the correcting chart with the step shift eliminated therefrom at three portions of the web paper. In addition, the printing heads for cyan (C), magenta (M), and yellow (Y) print correcting charts, respectively, on the three correcting charts for each color printed with the printing head for black (K). Thereafter, the correcting charts for three colors are captured with the inspecting unit. The controller determines the step shift of the printing heads for each color relative to the printing head for black (K) in the transportation direction, and determines the correction data for correcting a shift amount for each color in the transportation direction.
As noted above, the controller determines the step shift in the transportation direction of the printing head for black (K) only at a first correcting chart, and determines correction data for correcting the step shift. Thereafter, the controller determines the step shift in the transportation direction of the printing heads for each color relative to the printing head for black (K) by printing a second correcting chart for step-shift correction. Then, the controller determines correction data for correcting the step shift. In this manner, the step shift of the printing heads for every color upon printing is eliminated.
However, the example of the conventional apparatus with such a construction has the following drawback.
That is, the conventional apparatus needs two-time printing of the correcting chart, causing a low acquiring efficiency of the correction data for correcting the step shift. Such a problem may arise. The low acquiring efficiency causes more time to start printing of products, leading to decreased availability of the apparatus. Consequently, enhancing acquiring efficiency is an important task.